1. Technical Field of the Invention
This invention pertains in general to satellite-based broadcast data service. The invention pertains in particular to a method of enhancing the throughput of broadcast data service in communication systems utilizing satellites and multiple spot-beam coverage patterns.
2. Background of the Invention
Satellite broadcast technology has proven over a period of several decades to be an efficient and effective means of providing one-to-many data communication. Such service is usually provided using satellites in geostationary orbit, often referred to as “GEO” satellites. This approach has a lower complexity and, often, lower total system cost than other alternatives, due to the economies of scale associated with the broad field of view available at that orbit altitude.
Communication systems that use satellites in Low Earth Orbit (usually abbreviated to “LEO”) and Medium Earth Orbit (“MEO”) also exist. LEO-based systems, of which Iridium is perhaps the most successful example to date, are particularly well suited for two-way communication because of the reduced signal propagation time and power requirements associated with the lower orbit altitude. MEO-based systems can be optimized for either two-way or broadcast capability; the Global Positioning System (GPS) is a successful example of using a MEO constellation for a broadcast service.
While the reduced signal propagation time and power requirements of a LEO constellation offer strong advantages for two-way communication, those benefits are also applicable to broadcast services. The Iridium Mobile Satellite Services (MSS) system in particular, with its global coverage and multiple spot beams, has a great potential for carrying broadcast data. In fact, that system utilizes broadcast-oriented logical and physical channels to provide system information required for devices to access its two-way services. Refer to U.S. Pat. No. 5,410,728 for basic information about Iridium, and U.S. Pat. No. 5,574,968 for a detailed description of how Iridium uses broadcast channels to support two-way services.
Iridium also provides a one-way service, usually called Paging and sometimes referred to as Directed Messaging Service (DMS). Historically this capability has been used to send individually addressed numeric and text messages to specific receivers, using a high-power transmission as described in U.S. Pat. Nos. 5,603,079 and 5,613,194. A corporate profile associated with a company that was once responsible for operating the Iridium system, http://www.reuters.com/finance/stocks/companyProfile?symbol=IRIDQ.PK, identifies the paging service power level as having “a signal strength of approximately 26 dB,” as compared with the “signal strength for voice communication that averages approximately 16 dB.” This 10 dB advantage provides significant additional building penetration or signal reliability, depending on the receiver's needs and use cases.
With the well-known demise of one-way paging in general across the telecommunication industry, and the lack of new growth in Iridium Paging specifically (documented at http://www.iridium.com/SearchResults.aspx?q=paging by the current Iridium operating company), the associated resources are ripe for exploitation by a new broadcast service in which groups of users in multiple locations receive the same data sent just once in each relevant satellite spot beam. Since each spot beam of an Iridium satellite nominally covers an area that is approximately 250 miles in diameter, as noted in a document available from Iridium at http://www.iridium.com/DownloadAttachment.aspx?attachmentID=1197, such a service offers a significant potential for very large numbers of users to receive a single message broadcast using this capability, with minimal demands on the transmission capacity of the satellites.
It should be noted that this new broadcast service does not by itself require any inventive step for receiving devices. Simply creating multiple receiver devices with the same address is sufficient, and may already have been accomplished for unauthorized purposes through device “cloning,” a well-known practice that has plagued the wireless telecommunications industry since its inception. What is needed is a set of novel enhancements to this basic capability that, taken together, convert it from a hack to a genuine service.
It is thus a principal aim of the present invention to provide a system that supports broadcasting with global or regional scope, for groups of receivers located anywhere in the world whether in close proximity to one another or widely distributed, and offering multiple data services sourced by multiple data providers. It is a further aim of the present invention to increase the capacity of the underlying satellite transmission facility through a method that optimizes resource utilization using novel techniques and construction not found in the prior art.